Dear Chuck,
I think it helps to draw a distinction between a) feedback during the stroke; b) feedback at and as a result of impact; and c) the physics of momentum transfer from putterhead to ball. This helps clarify the issues.
Adding back weight in the top of the handle changes the overall weight of the putter, but in terms of physics, this added weight has little to do with the physics of momentum transfer. For that, the putter is very similar to a rock on a rope, and the mass of the putterhead itself is by far the most important aspect of the momentum delivered by a swinging putter. The back weight changes the overall weight, to be sure, but this doesn't change the "send" properties already inherent in the putterhead.
The added overall weight has three effects of note. First, the extra weight alters the natural tempo of the putter a little, by speeding it up. The tempo increases only a little, though, and this is hardly noticeable. Second, the added weight helps in the "hanging" of the arms and hands and keeping the hands low and inactive in the stroke. The heavier overall weight helps pull the hands low and keep them low. And third, the extra weight or mass has a tendency to stabilize the motion of the putter as it swings. It makes it a little harder to have irregular muscle action shift the putter out of its existing trajectory, given its extra inertia.
As to the two types of feedback, the back weighting effects both the feedback before impact and the feedback resulting from impact. before impact, the important feedback is when the putterhead moves too fast and causes the handle to waggle inside the grip of the hands. This waggling is mostly related to the mass of the putterhead, but it also relates to the swingweight. If the putter is "snatched" back from the ball at address, the hands move faster than the putterhead at first and this levers the handle against the back palm. If the putter is stopped too abruptly at the top of the backstroke, the mass in the putterhead tends to keep going, and this levers the handle against the front palm. Depending upon the flex properties of the shaft, the swingweight may exacerbate or diminish this waggling feedback. Without considering flex, the "heavier" swingweight tends to make the feedback during the stroke more pronounced. Taken to extremes, the proper putter would be one of the whippy putters, because the momentum of the putterhead needs to have a neutral effect on the handle with a good, natural tempo.
This being the case, what is the effect of the added back weight -- good or bad or indifferent? The added grip weight reduces the swingweight. How much? About every 6-7 grams of weight in the grip reduces 1 swingweight. The BCG system has standard inserts of 10, 30, and 50 grams. That would reduce swingweight by about 1.5, 5, and 8 swingweights. There seems to me to be sufficient "waggle" left at 10 and 30 grams, but 50 grams may be getting to be too much. I am currently experimenting with this to try to get a better understanding.
As to the second form of feedback, resulting from impact, the effect of the back weight is to alter the location of the "node" or cancellation point in the vibrations that travel up the shaft into the handle. Usually, the putter manufacturers using standard shafts and typical putterheads end up locating the cancellation point just an inch or so above the bottom of the grip material. This is usually too low for the golfer to benefit from the node. The benefit of the node is that placing the palms on the node results in a more "solid" feel at impact. The purpose of the BCG system is to move the node closer to the butt end of the shaft, and thus relocate the node up the handle to fit inside the golfers' normal grip position on the handle. The various characteristics of putters (some heavy heads, some flex differences in shafts, some heavier grip materials, some longer putters, etc.) mean that the 10 gram weight doesn't have the same effect in moving the node on different putters, so each golfer and putter really needs individual fitting to get the node and setup position of the hands on a specific putter set the best.
In the abstract, there is a question about the logic of suppressing feedback vibrations. As I understand it, the node simply denies the hands the feel of the vibrations that may have been felt. A poor shot has vibration X, and a good solid shot has vibration Y. When this is the case, the golfer pays attention to whether the vibrations are closer to X or to Y and learns from that. With the BCG system, however, the node would seem to cancel out the feel of good or bad vibrations. This would deem to fool the golfer with a bad vibration feeling just the same opr nearly the same as a solid putt with Y vibration. This line of thinking may be all wrong, so I will have to learn more about the system.
Since your American Putters are used by the Balance Certified Golf company to make their Mercury putters with the backweighting system, you are surely aware that this putter recently took top honors in two of the six or so categories judged by the Public Links magazine study of top putters. The competition included Scotty Cameron's Future putter and Robert Bettinardi's putter, and the Mercury putter took the "impact feel" and "distance control / touch" categories. So obviously the backweighting doesn't hurt the physics or the second sort of feedback. The first form of feedback, monitoring the waggling of the putter, really is important for the tempo. The tempo, in turn, is important for touch and accuracy. The presence of waggling would tend to effect the stroke path and face alignment adversely, so monitoring the tempo of the stroke is important for accuracy in making straight putts. The Scotty cameron putter was deemed the most "accurate" of the putters tested, but I wouldn't say the BCG system hurt the Mercury in this category. I've found very little adverse effect on accuracy of line with the BCG system in the Mercury putter. I also haven't found the Futura putter to be all that accurate, so I might very well disagree with the testers about the "accuracy" category.
Let me know if this leaves your questions unanswered.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
PuttingZone.com
http://puttingzone.com
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